I agree with you. I think that it was unfortunate that we did not get to see the characters fleshed out more through their interactions with each other and the environment.
Ashe is a unique heroine in the series, but I think that the way the game is structured, she is not comparable to other heroines in the series whose events revolve around them. The party could have gotten by with Ashe being a helpless diplomat or a sword-wielding cavalier. Do you know what I mean?